This invention relates to a polyamide (nylon) monofilament suture exhibiting improved properties, e.g., reduced energy and/or improved knot security, and to a process for its manufacture.
A considerable body of patent literature exists with regard to the manufacture of polyamide monofilaments. Illustrative of the many processes which have been developed over the years for the melt spinning of polyamide strands (filament, yarn, etc.) are those described in U.S. Pat. Nos. 2,212,772; 2,226,549; 3,091,015; 3,303,169; 3,345,445; 3,361,859; 3,379,810; 3,382,307; 3,577,500; 4,009,511; 4,374,797; 4,446,299; 4,461,740; 4,504,432; 4,504,545; 4,542,063; 4,578,451; 4,621,021; 4,624,816; 4,701,377; 4,758,472; 4,839,132; and, 4,859,389.
The manufacture of polyamide monofilaments which are intended for use as sutures is an established technology. U.S. Pat. No. 2,226,549 describes the melt spinning of polyhexamethylene adipamide (nylon 6,6) in which the resin is melt extruded and stretched to produce an oriented monofilament which is then heat treated to improve its recovery from deformation. A similar process resulting in a polyamide monofilament suture is described in U.S. Pat. No. 2,212,772. U.S. Pat. No. 4,578,451 describes a surgical filament manufactured from a copolyetheramide employing specific conditions for the extruding, quenching, drawing (stretching) and annealing operations.
One important characteristic of a suture is the amount of effort typically required to straighten the suture upon its removal from the package in order to ready the suture for use. In the case of a polyamide monofilament suture, this effort appears to be related to the "energy" of the suture, i.e., the integration of the stress-strain curve for the suture measured in kilograms, and is equivalent to the work expended in elongating the monofilament by a specified percentage of its original length. As the energy of a given size of polyamide monofilament suture is less so, too, the amount of effort required to straighten the suture prior to use is less.
Another important characteristic of a suture is its ability to retain a knot. In general, a suture exhibiting greater knot security is to be preferred to one exhibiting a lesser degree of knot security.